The spine is formed of a column of vertebra that extends between the cranium and pelvis. The three major sections of the spine are known as the cervical, thoracic and lumbar regions. There are 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae, with each of the 24 vertebrae being separated from each other by an intervertebral disc. A series of about 9 fused vertebrae extend from the lumbar region of the spine and make up the sacral and coccygeal regions of the vertebral column.
The main functions of the spine are to provide skeletal support and protect the spinal cord. Even slight disruptions to either the intervertebral discs or vertebrae can result in serious discomfort due to compression of nerve fibers either within the spinal cord or extending from the spinal cord. If a disruption to the spine becomes severe enough, damage to a nerve or part of the spinal cord may occur and can result in partial to total loss of bodily functions (e.g., walking, talking, breathing, etc.). Therefore, it is of great interest and concern to be able to treat and correct ailments of the spine.
When conservative efforts fail, treating spinal ailments very often includes a combination of spinal fusion and fixation. Generally, spinal fusion procedures involve removing some or all of an intervertebral disc, and inserting one or more intervertebral implants into the resulting disc space. Introducing the intervertebral implant serves to restore the height between adjacent vertebrae (“disc height”) and maintain the height and/or correct vertebral alignment issues until bone growth across the disc space connects the adjacent vertebral bodies. Fusions may be performed across a single level or multiple levels.
Often during spinal fusion procedures a posterior fixation construct is implanted to immobilize the vertebrae to be fused until the fusion is complete. The posterior fixation construct generally includes at least two bone anchors (e.g. pedicle screws, laminar hooks) connected together with a rod. Like the fusion, the fixation construct can be implanted across a single level or across multiple levels, and typically, the fixation system is positioned to at least span each level to be fused. These pedicle screw systems are very effective. However, there can also be challenges associated with them. For example, connecting the rod to each anchor can be difficult since the anchors are not necessarily coplanar. When this happens the rod must be bent to match the position of the anchor, or the entire vertebra must be moved to move the anchor to the rod. There are also instances when the position of the rod and/or the connecting portion of the anchor can obstruct access to spine in close proximity to the anchor.
The devices and methods described in the present application are directed at address these challenges.